Gear pump devolatilizing method and apparatus



April 1955 M. o. LONGSTRETH 3,177,127

GEAR PUMP DEVOLATILIZING METHOD AND APPARATUS Filed March 29, 1962 J0 12W m EXCHANGE/Q 94 h "91 United States Patent Murrey 0.

Midland, Mich., a corpora- Dow Chemical Company, tion of Delaware FiledMar. 29, 1962, Ser. No. 183,466 4 Claims. (Cl. 202-53) This inventionrelates to an improvement in a method and apparatus for devolatilizing apartial polymer solution.

The usual practice in devolatilizing a polymer solution, is to pump aheated partial polymer into a vessel by a number of different methods,removing the volatile under reduced atmospheric pressure, and pumpingthe devolatilized polymer out of the vessel.

The method and apparatus of the present invention represents animprovement over known methods and apparatus of the prior art. Briefly,the device of the invention comprises a gear pump assemblage closecoupled to a heat exchanger with means for depositing heated partialpolymer directly onto the surface of gears in the pump. A suitablevacuum connection is arranged on top of the pump for removing volatiles.

Among the more important advantages afforded by the device of theinvention, is that the problem of low temperature devolatilization ofheat sensitive materials is solved. By laying the partial polymerdirectly upon the moving gears, the inventory, or residence time in thedevolatilizer is reduced to a minimum, thus reducing the possibility ofdiscoloration. Allowing the pump to fill substantially independent oftemperature considerations, avoids flow of stifi devolatilized materialinto the pump from a reservoir. By operating at a minimum temperature,thermal degradation is also minimized. The invention is especially wellsuited for handling polymers of high viscosity.

The main object of this invention is to provide an improvement in amethod and a device for devolatilizing a partial polymer solution.

A more specific object is to provide a device adapted for the solutionof low temperature devolatilization of heat sensitive materials.

Still another object is to provide a device which reduces the inventory,or residence time of the polymer in the devolatilizer thus reducing thepossibility of discoloration.

Another object is to provide a device which fills independently oftemperature thus avoiding flow of stiff devolatilized material into thepump forming part of the device.

A further object is to control temperature so as to minimize thermaldegradation of a polymer during de'volatilization.

Other objects and features of the invention will become more apparentfrom the following description and accompanying drawing wherein:

FIG. 1 is a vertical section view of a devolatilizing pump assemblageembodying the principles of the invention; and

FIG. 2 is a section view generally as seen along line 2-2 in FIG. 1.

Numeral 6 identifies a devolatilizing pump assemblage which includes agear housing 8, and a vacuum chamber housing 10, mounted atop the gearhousing and secured thereto by fastening means, such as bolts 12,extending through flange means 14 and 16 provided on the housings 8 andrespectively. Polymer moving means in the form of a pair of herringbonegears 18 and 20, are positioned in the gear housing 8, so that the teethintermesh, the axis of each gear being located in a given horizontal"ice plane, as best seen in FIG. 1. The gear housing 8 has a centrallyarranged inlet opening 22, and an outlet opening 24 in axial alignmentwith the inlet opening. A threaded opening 26 is formed in a side wallof the gear housing 8, in a generally triangular region 27 defined by aline drawn tangent with the gear teeth extremities and a curved teethpro-file line of each gear, as illustrated in FIG. 1.

A pipe 28, threaded into the opening 26, is adapted to deliver a partialpolymer from a heat exchanger 30, into the gear housing. Power means(not shown) is coupled to the gear 18 via a shaft 32, whereby rotarymovement of the gears 18 and 20, is provided.

A side plate 34 may be removably aifixed to the gear housing 8 for theinstallation and removal of the gears 18 and 20. Secured to the lowerend of the gear housing 8, by fastening means such as bolts 36, is adischarge pipe 38, the latter being provided with a flange means 40coextensive with a flange means 42 formed integral with the gear housing8.

The vacuum chamber housing 10 is formed to provide an axially arrangedchamber 44 the lower end of which is coextensive with the gear housinginlet opening 22. A glass plate 46 may be mounted upon the housing 10,which plate serves as a window, or peep-hole for conveniently observingthe interior of the pump gear housing 8, and more particularly, thecondition of polymer being devolatilized therein. To maintain the glassplate 46 in secure position, a ring-like keeper plate 48 may be mountedatop the plate and held thereupon by fastening means, such as bolts 50,which extend through a flange 52 formed integral with the vacuum chamberhousing 10. An opening 54 is formed in a side wall of the housing 10,for receipt of a pipe 56 connected to a source of subatmosphericpressure to produce a vacuum condition in the housing; the volatiledrawn off of the polymer being treated, passes through the pipe 56 forcondensation by means (not shown), as is well known in the art.

In operating the pump assemblage 6, the partial polymer solution isdrawn from the heat exchanger 30 and admitted to the gear housing 8 inthe triangular region 27. The rate of flow of the solution, as well asthe temperature, are controlled so that the volatiles will be drawnquickly off before the devolatilized polymer is pumped out through theoutlet opening 24, by action of the gears 18 and 20.

It would serve no useful purpose to specify optimum operating pressuresand temperatures recommended when operating the device of the invention,since such would depend upon the specific material being processed, andquality of product desired, as will be appreciated. Suffice it to saythat for any given material being devolatilized, the pressure andtemperature should be such that a polymer of desired purity is produced.In other words, the sub-atmospheric pressure in the chamber housing 10and the temperature of the polymer stream being layed upon the gears 18and 20, should be such as to cause a flash-off of volatiles in theamount and at a rate which will produce a devolatilized polymer havingthe characteristics desired, especially regarding volatile content.

The foregoing description has been given in detail without thought oflimitation since the inventive principles involved are capable ofassuming other forms without departing from the spirit of the inventionor the scope of the following claims.

What is claimed is:

1. A low temperature method for removing volatiles from a partialpolymer solution of high viscosity comprising the steps of feeding astream of such polymer, after heating, directly onto tandemly arrangedintermeshing rotating gear means of a gear pump assemblage in the regionof intermesh While providing a sub-atmospheric pressure above said gearmeans, said feeding being substantially devoid of devolatilization untilsaid stream enters said region of intermesh, the rate of flow of saidstream to and said sub-atmospheric pressure above said gear means beingregulated to provide for quick removal of the volatiles from thesolution, and subsequently conducting the volatiles to a condensingmeans.

2. A low temperature method for removing volatiles from a partialpolymer solution of high viscosity comprising the steps of feeding astream of such polymer, after heating, directly onto tandemly arrangedintermeshing rotating gear means of a gear pump assemblage in thetriangular region defined by a line drawn tangent With the gear teethextremities and the curved teeth profile line of each gear whileproviding a sub-atmospheric pressure above said gear means, said feedingbeing substantially devoid of devolatilization until said stream islocated within said triangular region, the rate of flow of said streamto and said sub-atmospheric pressure above said gear means beingregulated to provide for quick removal of the volatiles from thesolution, and subsequently conducting the volatiles to a condensingmeans.

3. A devolatilizer for removing volatiles from a highly viscous partialpolymer product under low temperature conditions comprising, incombination, a gear housing, said housing having a lower polymer outletopening, a pair of intermeshing rotatable gears forming a gear pumpassemblage enclosed in said housing, means to rotate said gears, avacuum chamber aflixed to and in communication with the upper portion ofsaid gear housing, inlet means independent of said vacuum chamber toadmit said polymer solution into said gear housing directly onto saidgears, said inlet means opening into the triangular region defined by aline drawn tangent with the gear teeth extremities and the curved teethprofile line of each gear,

4. and outlet means for removing volatiles from said vacuum chamber.

4. .A devolatilizer for removing volatiles from a highly viscous partialpolymer product under low temperature conditions comprising, incombination, a gear housing, said housing having a lower polymer outletopening, a pair of intermeshing rotatable herringbone gears forming agear pump assemblage enclosed in said housing, means to rotate saidgears, a vacuum chamber afiixed to and in communication with the upperportion of said gear housing, inlet means to admit said polymer solutioninto said gear housing directly onto said gears, said inlet meansindependent of said vacuum chamber opening into the triangular regiondefined by a line drawn tangent with the gear teeth extremities and thecurved teeth profile line of each gear, and outlet means for removingvolatiles from said vacuum chamber.

References Cited by the Examiner UNITED STATES PATENTS 1,156,096 10/15Price 159-2 1,614,526 1/27 Lambie et al. 2,205,328 6/40 Wills. 2,276,2613/42 Buzard. 2,298,644 10/42 Hummel. 2,572,063 10/51 Skipper.

FOREIGN PATENTS 324,648 1/30 Great Britain.

369,658 2/23 Germany.

373,676 4/22 Germany.

NORMAN YUDKOFF, Primary Examiner. GEORGE D. MITCHELL, Examiner.

1. A LOW TEMPERATURE METHOD FOR REMOVING VOLATILES FROM A PARTIALPOLYMER SOLUTION OF HIGH VISCOSITY COMPRISING THE STEPS OF FEEDING ASTREAM OF SUCH POLYMER, AFTER HEATING, DIRECTLY ONTO TANDEMLY ARRANGEDINTERMESHING ROTATING GEAR MEANS OF A GEAR PUMP ASSEMBLAGE IN THE REGIONOF INTERMESH WHILE PROVIDING A SUB-ATMOSPHERIC PRESSURE ABOVE SAID GEARMEANS, SAID FEEDING BEING SUBSTANTIALLY DEVOID OF DEVOLATILIZATION UNTILSAID STREAM ENTERS SAID REGION OF INTERMESH, THE RATE OF FLOW OF SAIDSTREAM TO AND SAID SUB-ATMOSPHERIC PRESSURE ABOVE SAID GEAR MEANS BEINGREGULATED TO PROVIDE FOR QUICK REMOVAL OF THE VOLATILES FROM THESOLUTION, AND SUBSEQUENTLY CONDUCTING THE VOLATILES TO A CONDENSINGMEANS.